In France, the numbering system for school years counts down and not up.
If your stepson was still 13 at the start of the current school year, he will be in the 4th grade at a 'coll�ge'. If he was already 14 at the start of the school, he will be in the 3rd grade. This is the final year at a coll�ge. (It's equivalent to our Year 10 or the old 4th form).
There are no public examinations at the end of coll�ge education. (So there is no equivalent to our GCSEs). After attending a coll�ge, your stepson will transfer, at the age of 15, to a 'lyc�e'. This is roughly equivalent to our 6th form college but with a start one year earlier and a duration of three years rather than two. The years are referred to as 2nd grade, 1st grade and Final grade. Students study for the Baccalaur�at which covers a much wider area of study than British A-level exams. There are actually three different types of Baccalaur�at, technological, professional and general but most students study for the general syllabus. While this offers the opportunity to specialise in certain areas, it's impossible to follow an 'all arts' or 'all sciences' path, as many British A-level students currently do. (Many British schools and colleges are currently seeking to replace A-levels with the International Baccalaur�at for precisely this reason).
While studying for the Baccalaur�at, your stepson (irrespective of his chosen specialisms) will have to study certain elements of science, mathematics, economics, social science, literature and philosophy. The Baccalaur�at is internationally accepted (far more so than A-levels) and recognised for entry into British universities.
Chris